The present invention relates to the field of optometric examinations for video display terminal (VDT) users in order to prescribe spectacles for use when working with a VDT.
An increasing number of people spend numerous hours a day looking at a video display terminal (VDT), such as a computer screen. Whether used for business, entertainment, pleasure, research, or other reasons, prolonged time spent focusing on a VDT can lead to considerable eye strain. As the use of VDTs becomes even more widespread, so too have a number of ophthalmological afflictions caused by their use. These afflictions are often manifested as headaches, neck or shoulder pain, tired eyes, color fringes, blurred vision, double vision, changes in prescription over time, or loss of focus. The alphanumeric and graphic characters comprising a typical VDT image present a Gaussian light distribution and do not have clearly defined edges. Without clearly defined edges, the characters on a VDT make it difficult for the eyes to focus.
VDT users typically maintain a distance of 40-60 cm from VDTs. Viewing a VDT from this distance causes significant amounts of stress and fatigue on the eyes. These problems, exacerbated by the numerous hours that many VDT users spend looking at VDTs, cause peculiar eye problems requiring prescription spectacles specifically selected to treat and prevent the resulting afflictions.
To determine accurate prescriptions for VDT users, test equipment and procedures must be adopted to simulate an actual VDT. Without a way to examine the eyes using an image that accurately simulates the actual conditions under which the eyes are forced to perform, a reliable prescription for corrective lenses cannot be determined.
The traditional process used by medical practitioners to assess the need for corrective lenses involves placing an apparatus called a phoropter in front of the patient that enables the doctor quickly to change lenses while asking the patient to choose which lens performs the best. As the doctor changes lenses, the patient looks through the apparatus to focus on a test image. The doctor also uses a retinoscope to assess the degree of relaxation of the eye muscles. The doctor uses this information to determine a combination of lenses and a prescription that provides the greatest relaxation for the eye muscles.
However, if the image upon which the doctor has the patient focus does not accurately simulate the actual operating conditions under which the patient""s eyes will be forced to perform, the prescription cannot be determined reliably. Traditional forms of testing equipment, including nearpoint cards and projections on walls, do not provide satisfactory simulation of actual operating conditions for VDT users. Essentially, a doctor is compelled to guess the prescription and let the patient take and try the spectacles to determine if they are satisfactory. If they are not satisfactory, the patient has to return to the doctor and the process is repeated until a satisfactory prescription is achieved. This process is inefficient, wasting valuable time and energy.
Even systems designed specifically for conducting optometric exams on VDT users do not provide optimal simulation of a modern, high-resolution VDT. Examples of such systems include those represented by U.S. Pat. Nos. 4,576,454; 4,998,820; 5,191,367; and 5,325,136. One problem with those systems is that they only use test images that depict alphanumeric characters represented in a dot-matrix format. The dot-matrix format is displayed by constructing a display screen comprising a printed layer with sets of small circular openings that cooperatively define alphanumeric characters in terms of pixel-like elements of light from a light source positioned behind the screen. This dot-matrix format poorly simulates the high-resolution displays of modern VDTs. In modern, high-resolution VDTs, in which display screen resolution can be on the order of 1200 dpi, individual pixels are so small that they cooperatively appear to form continuous lines without intervening spaces or gaps. These seemingly continuous characters are poorly simulated by the dot-matrix characters of prior devices.
Another problem with simulating a modern VDT image is that previous systems teach only alphanumeric images; they do not depict graphical images similar to those found on modern VDTs. Because of their poor simulation of modern VDTs, the previous systems do not allow for an accurate examination of the eyes of VDT users. Achieving the most accurate examination can only be accomplished though use of a vision tester display screen that accurately simulates modern, high-resolution VDTs. That is the primary purpose of the present invention.
One embodiment of the present invention generally comprises a display screen and vision tester apparatus, as well as a method, for use in optometric examinations to simulate the actual alphanumeric and graphic images emitted by a modern, high-resolution video display terminal (VDT) and to facilitate prescribing corrective lenses that will perform well for a patient using a VDT.
In a preferred embodiment, the display screen is constructed of multiple layers of plastic sheets with different indexes of refraction. These sheets refract light supplied by the vision tester so as to present light with a Gaussian profile typical of light emitted from pixels in modern, high-resolution VDTs.
The display screen in a preferred embodiment also includes an optional, substantially translucent layer of color. Multiple colors can be used. As used in this specification and the attached claims, the term xe2x80x9ccolorxe2x80x9d includes typical colors, black and white, and shades of gray. By applying a layer of one or more colors to the plastic sheets, various colored alphanumeric and graphical images can be formed on the display screen. A mask layer allows light to be transmitted through predetermined patterns so that alphanumeric characters can be formed using continuous lines, rather than a matrix of small circular openings. This provides an accurate simulation of modern, high-resolution VDTs. Similarly, a high-resolution VDT is accurately emulated through the diverse graphical images that can be displayed by this invention. For example, these graphic displays can depict computer icons, window-shaped computer user interfaces, or similar designs.
One distinct advantage of this invention is that specific images can be displayed in support of a desired optometric test. For example, a preferred embodiment of this invention displays a red image and a green image horizontally spaced. The combination of the red and green images allows for a Red-Green Bichrome Test to be conducted by a doctor.
Additional objects and advantages of this invention will be apparent from the following detailed description of a preferred embodiment thereof which proceeds with reference to the accompanying drawings.